A wide variety of sensors are being developed as sensors for detecting physical quantities such as temperature, humidity, air pressure, and light intensity. Particularly, in recent years, sensors referred to as MEMS (Micro Electro Mechanical Systems) with small sizes and low power consumption (hereinafter, also referred to as MEMS sensors) are attracting attention. Since a MEMS sensor with a small size and low power consumption can be readily provided in plurality, sensor units equipped with a wide variety of sensors can be constructed.
Such a sensor unit is capable of compositely sensing an environment such as a work space or a residential space and acquiring various types of information exemplified by information related to energy such as power, biometric information, and environmental information. In addition, through such information, the sensor unit is able to supporting diversified information analysis and utilization.
With a sensor unit including a plurality of sensors as described above, even when power consumption of each individual sensor is low, high power consumption of the unit as a whole may become an issue. In particular, when a battery is adopted as a power supply due to constraints on installation and the like, power consumption is desirably minimized. For example, once a sensor unit is installed and collection, accumulation, and transmission of environmental data commence, since the sensor unit is desirably driven for as long a period as possible without having to replace the battery, power consumption must be kept low. When power consumption cannot be kept low and a frequency of battery replacement is high, maintenance costs for replacing batteries are incurred. The incurrence of such maintenance costs poses a barrier to introduction of sensors.
PTL 1 proposes a system which varies sleep time of a wireless sensor in accordance with an operational state of equipment (air conditioning). In the system proposed in PTL 1, battery consumption is suppressed by setting a short sleep time of the sensor when the equipment (air conditioning) is operational and setting a long sleep time of the sensor when the equipment (air conditioning) is not operational.
PTL 2 proposes a wireless management system which awakes a control section in a sleep state when a time of day set in advance arrives to transmit acquired data and receive commands addressed to the system's own apparatus and which makes a transition to a sleep state when receiving a sleep command addressed to the system's own apparatus. Accordingly, even when a plurality of systems are arranged at scattered outdoor locations, the systems can be stably operated with batteries over a long period of time.
PTL 3 proposes a wireless distance detection system which includes a power saving mode in which an inquiry is made once every minute and an attention-required mode in which the inquiry is made six times per minute, and when motion of a mobile terminal is detected by an acceleration sensor, intervals at which inquiries are made are shortened.
As described above, conventional systems are designed to save power by controlling sensors to either operate or sleep in accordance with specific conditions. However, depending on situations, power saving cannot be appropriately achieved by controlling sensors in accordance with specific conditions. In particular, when performing composite sensing using a plurality of sensors, it is difficult to appropriately control all of the sensors under a single condition.